1. Field of the Invention
The present invention relates to an apparatus and method for loading wafers into a processing system. More particularly, the invention relates to a method and apparatus for accessing a wafer pod or cassette so that wafers can be moved between the wafer pod and the processing system.
2. Background of the Related Art
The fabrication of electronic devices on substrates is typically performed in processing systems. Processing systems take on various configurations including single wafer systems where a single wafer is processed in a processing chamber and batch type systems where multiple wafers are processed in a chamber. Despite system architecture disparities, substrates are delivered to the processing systems from a clean room using standardized interfaces and wafer pods or cassettes. A human operator or factory automation delivers multiple wafers loaded in wafer pods or cassettes to a loading mechanism which transfers the wafers from the clean room in a fabrication facility into the processing system without exposing the wafers to contaminants. The delivery of wafers between processing systems and the operation of pod doors has been standardized by an organization known as SEMI.
Recent advances in circuit design and processing technology have driven a significant decrease in the size of semiconductor devices. At the same time, chip makers are trying to increase the number of devices which can be produced on a single wafer. Accordingly, wafer sizes have increased to 300 mm, thereby requiring larger systems which increase the amount of fabrication facility floor space required to house the larger systems. Also, as the wafer size has increased, the handling of wafers has become more limited to factory automation, instead of manual handling, to accommodate the increase in size and weight of wafer pods.
FIG. 1 is a schematic top view of a representative processing system 10 having a front-end staging area 12 which mounts a plurality of wafer pod loading stations 14 through an interface wall 16 separating the clean room 18 from the gray area 20 where the processing system 10 is housed. A single wafer processing system may include one or more load lock chambers 22, a central transfer chamber 24 and a plurality of processing chambers 26 mounted on the transfer chamber.
A robot 28 disposed in the front-end staging area 12 moves wafers from wafer pods disposed on the pod loading stations 14 into a load lock chamber 22. A robot 30 disposed in the transfer chamber 24 moves wafers from a load lock chamber 22 into a processing chamber 26. The pod loading stations 14 are disposed through an opening in the interface wall 16 and provide a movable door opener 32 which seals the opening in the interface wall 16 when a wafer pod is not positioned on the pod loading station 14.
There are several commercial pod loading stations available from manufacturers such as Jenoptik/INFAB, ASYST, PRI Automation and DYFUKU. These pod loading stations are very similar in function and appearance as they are all designed to meet applicable SEMI standards for the interface to the processing system as well as the interface to the pod and the pod loading station as presented to the fabrication facility material transport system (AGV, OHT, PGV). These current designs share the following details: a mechanical interface to receive a pod using three pins as required by SEMI; a mechanism to latch the pod into place on the pod loader; a mechanism to grip a pod door and operate the pod door latch mechanism; and, a mechanism to remove the pod door and store the door out of the way of the pod opening to allow clear access to the wafers stored inside the pod. These existing designs all employ a mechanical motion which latches the pod to a fixed position, grips and unlatches the pod door, pulls the pod door horizontally away from the pod (i.e., into the staging area 12), and then lowers the pod door below the plane of the pod for storage of the door while allowing access to all wafer positions.
The pod loading stations 14 are designed so that an operator or factory automation can deliver a wafer pod onto the pod loading station and the wafers can be unloaded into the processing system. FIG. 2 is a schematic side view of a pod loading station 14 illustrating the state of the art prior to the present invention. The loading station typically includes a pod receiving platform 40 which is movable in a horizontal plane to receive a pod 60 in a first position away from the interface wall 16 and then move the pod into a loading/unloading position adjacent the interface wall. The wafer pods have a door which includes a locking mechanism to secure the door in place in the pod for transit within the fabrication facility. The locking mechanism is standardized as required by SEMI and includes two rotating latches to secure the door in a locked position. The pod loading stations 14 include a door opening mechanism 42 which engages and operates the locking mechanisms of the door and then opens the door when the wafer pod is in the loading/unloading position. The door opening mechanism 42 presently used is disposed in the front-end staging area 12 and moves the door horizontally away from the wafer pod along arrow A until the door clears the pod opening and then vertically downward along arrow B until the pod opening is cleared enabling horizontal access to wafers in the pod. Both the location of the door opener 42 and the horizontal motion required to remove the door consume additional floor space in the front-end staging area, thereby increasing the overall footprint of the system.
Each of the pod loading stations currently in use require both the horizontal and vertical movement of the door in order to open the pod. This type of mechanism requires a clearance space or envelope within the front-end staging area 12 to enable the pod door to be opened which adds a significant cost to the facility in terms of floor space required for a system. Additionally, the initial movement of the door opening mechanism is a hinged movement which causes some frictional contact between the pod door and the pod opening. It would be desirable if the pod loading station would open pod doors with minimal friction and using simple actuator motions.
Therefore, there is a need for a pod loading station which occupies minimal floor space and utilizes fewer movements than currently available designs.